1. Technical Field
The present invention relates to a sheet loading apparatus for loading and supporting the sheet, such as a document or a recording sheet to be supplied to an image forming apparatus as, for example, a printer, a copying machine, a facsimile, or the like.
2. Related Art
An image forming apparatus has generally been provided with a sheet feeding means for feeding a sheet to an image forming means of the apparatus and said sheet feeding means includes a sheet loading apparatus for loading and supporting the sheet.
The sheet loading apparatus is provided with a sheet cassette which can accommodate a plurality of sheets and can be loaded or unloaded to or from the apparatus body. The sheet cassette is comprised of a cassette tray having a vertically movable sheet loading plate wherein a feed roller mounted on the side of the apparatus body is operative to press the sheets loaded in the cassette and feed them from the cassette. A lateral positioning device for the sheets (sheet guides) is also provided for regulating the lateral positioning of the sheets in the width direction of the cassette.
This sheet guide device is provided at the bottom of the cassette tray and can have its position changed depending on the width of the sheets having different sizes by positioning the guides in cutout portions (apertures) formed in the sheet loading pate. However, the sheet loading apparatus of the related art has the following principle problems. The cutout portions (apertures), through which the width regulating members connected to the sheet loading plate extend, open to a great extent to change the position of the width regulating members to accommodate sheets of various sizes. Meanwhile, the sheet loading plate engages the cassette by means of a cutout portion provided at the bottom of the cassette tray wherein one end of the sheet loading plate is inserted in the cutout portion. Since a certain amount of play occurs with regard to this engagement, a certain amount of play also exists in the feeding direction of the sheet from the sheet loading plate and in the width regulating member provided at the bottom of the cassette tray. As a result, sheet discharges from the cassette diagonally or the sheet supply path is shifted in the width direction when the sheets loaded on the sheet loading plate are each moved upward for pressing to the feed roller and the sheet is transferred by the feed roller.
Moreover, even when the width regulating member is opened externally or tilted oppositely to the inside of the cassette tray, the printing position of a sheet is also shifted because the position in the width direction of sheets loaded on the sheet loading plate is displaced. However, since the width regulating member is provided on the cassette body, position adjustment has to be performed on the sheet loading apparatus fitting rail and stopper in order to prevent diagonal running and positional displacement of sheet, but here rises problems that the adjustment range is small and the rail structure is complicated. Moreover, a fitting position error of the sheet loading apparatus in an image forming apparatus also results in the problem that the sheet position in the lateral direction is shifted because the sheet feeding direction is at a right angle to the fitting direction of the sheet loading apparatus.